From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from rock.gnat.com (rock.gnat.com [IPv6:2620:20:4000:0:a9e:1ff:fe9b:1d1]) by sourceware.org (Postfix) with ESMTPS id DB920383DBA9; Wed, 22 Jun 2022 00:20:53 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org DB920383DBA9 Received: from localhost (localhost.localdomain [127.0.0.1]) by filtered-rock.gnat.com (Postfix) with ESMTP id EECCF1160F1; Tue, 21 Jun 2022 20:20:51 -0400 (EDT) X-Virus-Scanned: Debian amavisd-new at gnat.com Received: from rock.gnat.com ([127.0.0.1]) by localhost (rock.gnat.com [127.0.0.1]) (amavisd-new, port 10024) with LMTP id ZC3+qDmt29Dv; Tue, 21 Jun 2022 20:20:51 -0400 (EDT) Received: from free.home (tron.gnat.com [IPv6:2620:20:4000:0:46a8:42ff:fe0e:e294]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by rock.gnat.com (Postfix) with ESMTPS id 869C91160D2; Tue, 21 Jun 2022 20:20:51 -0400 (EDT) Received: from livre (livre.home [172.31.160.2]) by free.home (8.15.2/8.15.2) with ESMTPS id 25M0KhqY716704 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 21 Jun 2022 21:20:44 -0300 From: Alexandre Oliva To: Jonathan Wakely Cc: gcc Patches , "libstdc++" Subject: Re: [PATCH] libstdc++: testsuite: call sched_yield for nonpreemptive targets Organization: Free thinker, does not speak for AdaCore References: Errors-To: aoliva@lxoliva.fsfla.org Date: Tue, 21 Jun 2022 21:20:43 -0300 In-Reply-To: (Jonathan Wakely's message of "Tue, 21 Jun 2022 08:38:47 +0100") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.84 X-Spam-Status: No, score=-6.3 required=5.0 tests=BAYES_00, KAM_DMARC_STATUS, SPF_HELO_NONE, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: libstdc++@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libstdc++ mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 22 Jun 2022 00:20:56 -0000 On Jun 21, 2022, Jonathan Wakely wrote: > On Tue, 21 Jun 2022 at 06:54, Alexandre Oliva via Libstdc++ > wrote: >> >> >> As in the gcc testsuite, systems without preemptive multi-threading >> require sched_yield calls to be placed at points in which a context >> switch might be needed to enable the test to complete. > I'll try to remember that, but will probably forget. Is this really > the only affected test? Yeah, the only one in libstdc++-v3/testsuite, as of gcc-11, which is what I've focused on for this project; I haven't gone through all fails on master to make sure they're unrelated. (This is holding up some filesystem-related patches, whose tests are failing for reasons not present in gcc-11, and some of the forward-ports needed significant rewriting.) libstdc++ has plenty of threading tests, but they involve sleeping or otherwise blocking, which offers a context switch opportunity even on non-preemptive multithreading systems. It's busy waits that require a sched_yield. The gcc testsuite has a handful of those; covered by a separate patch also posted last night. -- Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/ Free Software Activist GNU Toolchain Engineer Disinformation flourishes because many people care deeply about injustice but very few check the facts. Ask me about